Circuit arrangement for accelerated continuous cleaning of self cleaning oven coatings

ABSTRACT

A circuit arrangement for a continuously cleaning coated oven at an elevated temperature range above the normal operating range but not in excess of that allowed for non-locked oven operation so as to improve the thermal cleaning of the oven bottom wall coating. The arrangement includes a separate manually settable control switch having a Cook position for energizing the bake and broil elements in a conventional manner and a Clean position wherein the broil element is disconnected and the bake element is energized while maintaining the thermostatic condition for broil operation such that the oven will continuously self-clean by heating the oven bottom wall much hotter than the existing oven air temperature.

United States Patent Fry et al.

[54] CIRCUIT ARRANGEMENT FOR ACCELERATED CONTINUOUS e CLEANING OF SELFCLEANING OVEN COATINGS [72] Inventors: Millard E. Fry; Robert D. Bremer,both of 1 Dayton, Ohio [73] Assignee: General Motors Corporation,Detroit,

Mich. 1

[22] Filed: June 16, 1971 [21] Appl.No.: 153,727

52 U.S. c1 ..219 413, 219/396, 219/397 511 1111. C1 ..F27d 11 00 [58]Field of Search ..2l9/396-398, 391,

[56] References Cited UNITED STATES PATENTS 3,036,192 5/1962 Fry..219/39.1 3,121,158 2/1964 Hurko.. ...219/397 3,266,477 8/1966 Stiles..126/19 1 yJune6, 1972 3,301,999 1/1967 Chisholm ..2 19/396 X 3,302,0001/1967 Sherman... .....2l9/393 3,350,542 10/1967 Actman..;. ..2l9/4l23,342,976 9/1967 Kjellberg ..219/413 3,353,004 11/1967 Alexander .219/398 Primary ExaminerVolodymyr Y. Mayewsky Attorney-William S.Pettigrew [57] ABSTRACT A circuit arrangement for a continuouslycleaning coated oven at an elevated temperature range above the normaloperating range but not in excess of that allowed for nonlocked ovenoperation so as to improve the thermal cleaning of the oven bottom wallcoating, The arrangement includes a separate manually settable controlswitch having a Cook position for energizing the bake and broil elementsin a conventional manner and a Clean position wherein the broil elementis disconnected and the bake element is energized while maintaining thethermostatic condition for broil operation such that the oven willcontinuously self-clean by heating the oven bottom wall much hotter thanthe existing oven air temperature.

3 Claims, 3 Drawing figures soiled oven bottom wall or liner shoulddividually controlled by The present invention relates to an improvedcontrol system for a low-temperature self-cleaning oven, andparticularly to an accelerated continuously cleaning or low temperaturethermal cleaning ceramic coated oven suited for domestic use in thekitchen. As discussed in an article in Appliance Magazine dated December1970, pages 52-55, the development and advent of oven coatings whichwill continuously clean at normal oven operating temperatures hasprogressed to providing the range industry with a ceramic coating ofversatile use at normal operating temperatures that will nearlyeliminate the work of keeping the oven areas clean. The term lowtemperature thermal cleaning oven coating is defined to differentiatebetween an oven to whichv a continuous or thermal cleaning coating isapplied to the oven walls requires the elevated temperature of 880 F.and higher to degrade oven wall soils. It has been found incontinuouscleaning ovens that an increase in normal oven operating temperaturesfrom that of 350 to 450 or 550 F. is beneficial to the thermal cleaningprocess and especially the usually heavily be subjected to highertemperatures to promote the oxidation of the soil by the coating andthus the cleaning in this area. I

It is an object of the present invention to provide a continuouscleaning coated oven wherein elevated temperatures can be obtained in aconventional oven having an upper heating unit to supply heat forbrolling operations and a lower heating unit to supply heat for bakingoperations by a circuit arrangement providing a cleaning operation thatdisconnects the broil unit and energizes the bake unit with thethermostat conditions for broil operation so that the oven bottom wallwill be heated much hotter than the existing oven air temperature so asto increase the efficiency of the continuously cleaning coating on thebottom wall of the oven.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the Drawings:

FIG. 1 is a front perspective view of aneye-level oven including theinner walls of the oven cavity coated with an oxidizing continuouslycleaning coating;

FIG. 2 is a schematic wiring diagram of the control circuit for theoven:

FIG. 3 is a cycle chart showing the positioning of the various switchcontacts in the diagram of FIG. 2.

Referring now to the drawings and in particular FIG. 1, there is shownfor illustrative purposes an eye-level or mounted electric oven having abox-like configuration with an outer oven housing 12 and an innercooking cavity or compartment l4 defined by frame opening 16 having adoor, partially indicated at 17, hingedly mounted for closing the frontopening 16 of the oven 10. The oven includes supporting racks 20 on theside walls of shelves (not shown) which in turn are utilized tosupporting cooking utensils within the oven. For providing the necessarycooking operations a bake element 24 is positioned adjacent the bottomwall 26 of the ovenwhile a broil element 28 is supported near the topwall 29 of the oven.

To enhance the convenience and utility of the oven 10 a lamp housing 30is positioned within the oven designed in a manner that the light willshow downwardly into the oven. A conventional thermostat, shownschematically at 31 in FlG. 2, includes a temperature sensor in the formof an oven thermostat bulb 33 positioned near the top wall 29 adjacentthe broil element 28. It is standard 33 adjacent the broil element 28 asthe highest wattages normally developed by the heating elements are inthe broil element. At the right of the oven is a front control panel 32in which the upper and lower heating elements may be inan oventhermostat switch knob 34,

practice to locate the sensing bulb 22 thereof for supporting aplurality an oven timer 36 and the like which are standard in this art.it should be noted that coated oven liners may be slidably removed fromthe oven cavity 14 through the frame opening such as disclosed in US.Pat. No. 3,036,192 issued May 22, 1962 to M. E. Fry and assigned to thesame assignee as the instant application.

In the preferred embodiment the exposed surfaces of the oven walls arecoated with a self-cleaning ceramic coating having the characteristic ofoxidizing oven food soils thereon in the temperature range between 400and 600 Magazine article test results have shown that while thermalcoatings do eliminate food soil at normal operating temperabeneficial tothe cleaning process with the usually heavily soiled oven bottom wallrequiring a temperature approaching 700 F. to clean this area.

The present invention is directed to the concept of accelerating thecleaning of the coating and particularly the of the standard bakingelement 24 of the oven. The hydraulic thennostat 31 controls the heatingor cooling of the oven elements 24 and 28 to maintain the temperatureselected for all baking operations. Whenelement 24 produces no heat. Forbroiling, the broil element heats continuously except in unusual casessuch as when the door is closed. In that case the thermostat sensingbulb, located adjacent the broil eleprevent the oven ambient temperaturefrom exceeding the broil setting which is approximately 580 F. in thedisclosed form.

As seen in FIG. 2 the thermostat 31 includes a pair of contacts,generally indicated at D, opened and closed by switches 38 and 40closing fixed pairs of contacts 50, 51 and 52, 53 respectively. Theswitches 38, 40 are cycled intermittently by and the sensing bulb 33within the oven. The rate at which the contact Group D, indicated bycontacts 38 and 40, are cycled is dependent upon the presetting of thestandard oven temperature control knob 34, the preset temperature beingsensed by the bulb 33 within the oven. vThus if the knob 34 is set for325 F. the cycling contacts 38 and 40 will open and close to maintainthe selected temperature (325 F.) within the oven.

The foregoing description has set forth only the conventionaltemperature response oven control thermostats which are well known inthe art and such switch may,

for broil such that the oven bottom wall will be subjected to a hightemperature in the range of 700 F. while the oven ambient temperaturewill not exceed 600 F.

Turning now to those components related to the oven cleaning cycle aselector switch assembly 60 is provided including a pair of heatingelement transfer (double pole-double throw) switches R and S whichconnect the broil heating element 28 for example,

and the bake heating element 24 in a particular manner to the source ofpower L,,' N and L2 depending upon whether a broil" or bake COOKoperation or accelerated CLEAN operation is to be effected. Moreparticularly and with the user settable knob 34 in the variabletemperature bake position switch R on contact R, connects the broilelement 28 through the oven thermostat contact C across L and N toll8-volt power and switch S contact S thereby connecting the bakeelement 24 across line conductors L, and L to 236- volt power to provideheat energy for the baking function of the COOK operation thermallycycled at contact group D. As an example, 3,800 watts of heat energy maybe provided during the bake function comprising 3,000 watts from'thebake element 24 and 800 from the broil element 28. 1

With the user settable knob 34 in the broil position (580 F.) the bakeunit 24 is deenergized and switch R on contact R, connects the broilelement 28 through the oven thermostat switch across L, and L to236-volt power to provide heat energy for the-broiling function of theCOOK operation which may be thermally cycled at D. Specifically, 3,200watts of heat energy may be provided during the "broil". function, allfrom the broil element 28 since nected at contact For the CLEANoperation the selector switch assembly 60 is manually operated by aswitch 48 on panel 32 to position the transfer switches R and S oncontacts R and 8,, respectively. Thus, the broil element is disconnectedwhile the bake element 24 is connected through the thermostat 31 acrossL,, L to 236-volt'powe'r cycled on both sides of the line by the thermalrelay switches D.

Tracing the circuit in detail the bake operation contacts A and C areclosed positively while contacts D are cycling in accordance with thetemperature within the oven as prescribed by the setting on knob or dial34. As the cycle is inthe bake element 24 is discon- -itiated, theheating elements 24 and 28 will be energized as follows: from L, throughfirst circuit means including terminal 51 fixed contact 51, firstcycling thermostat contact 38, fixed contact 50, terminal 50, line 54,to the junction 55 of the broil heating element 28 and the bake heatingelement 24.

From this point 55, the broil element 28 will be energized by way ofline 56,-switch S through contact 5,, line 57, terminal 58, cam actuatedswitch blade 59 and movable'contact C to fixed contact 61 and terminal62 to the neutral side line N, thus placing the'broil element 28 onll8-volt operation. At the same time, the bake heating element 24 willbe energized from the junction point 55, line 71, switch R, contact R,,line .72, terminal 73, switch blade 74, movable contact A, fixed contact63, line 75, terminal 53, fixed contact 53', second thermostat cyclingcontact 40, fixed contact 52, terminal 52 to the other side of the lineL thereby placing the bake element 24 on 236-volt operation. For thebroil operation the cam operated movable contact B engages fixed contact64 leading to junction 65 and placing the broil element 28 across thelines L,, L through cycling contacts D. The path of second circuit meansfor L includes terminal 52', fixed contact 52, second cycling thermostatcontact 40, fixed contact 53, terminal 53, line 75 to junction 65 whichconnects first fixed bake contact 63 and fixed broil contact 64. Thefirst fixed bake contact 63 is connected via first movable cam operatedcontact A, line 74, terminal 73 and line 72 to cook" contact R, of thetransfer. switch while the fixed broil contact 64 is connected viamovable contact 8, line 59, terminal 58 and line 57 to cook contact 8,.Third circuit means connect neutral line N to a second fixed bakecontact 61 and thence via movable contact C, line 59, terminal 58 andline 57 to .cook" contact 8,.

As the CLEAN operation is initiated the heating element 24 will beenergized as follows: from L, through terminal 51', contacts 51, 38 and50, terminal 50', line 54 to the junction point 55 of theelernents 24and 28. From this point 55, the

- bake element 24 will be energized by way of line 71, switch R contactR line 80, contact 8,, line57, terminal 58, line 59, movable contact B,fixed broil contact 64, junction 65, line 75, terminal 53', fixedcontact 53, cycling thermostat contact 40, fixed contact 52 and terminal52' to the other side of the line L thereby placing the bake element 24on 236-volt operation. It will be noted that interconnected transferswitches R and S have a line 81 interconnecting the contact R, with thecontact 8, while the line 80 interconnects the contact S, with thecontact R The arrangement of the accelerated CLEAN position of theselector switch allows the broil element 28 to be disconnected and thebake element 24 to be energized with the thermostat conditioned forbroil operation. Thus, the heat generated by the bake element 24 willact upon the bottom wall 26 of the oven to insure a thermal cleaningaction on the coating. The oven chamber also has its side, top and backwalls subjected to an elevated temperature between about 500 F. andabout 600 F. which will allow accelerated cleaning of the coatingthereon for improved soil removal.

A typical set of instructions for use with the instant invention wouldread as follows:

After heavy soilingrapid cleanup may be desired. A 5-hour cycle isrecommended. This may be done at night.

ACCELERATED CLEANING 1. Move switch on console top to Clean. 2. Set stoptime on timer.

3. Set cooking hours to 5.

4. Set oven thermostat to Broil.

AFTER CLEANING 1. Return thermostat to Off.

2. Return cooking hours to Manual.

3. Return switch on console top to Cook.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted. I

What is claimed is: t

l. A continuously cleaning oven comprising an outer oven housingenclosing walls defining a bake and broil compartment, said compartmenthaving a bottom wall, opposite side walls, a door for closing saidcompartment,a rear wall and a top wall, a thermal cleaning coating onthe exposed surface of at least said bottom wall, and having thecharacteristic of oxidizing oven food soils thereon in the oventemperature range of between 400 and 600 jacent the bottom wall and abroiling element supported adjacent the top wall of the compartment,control means for said bake and broil elements settable in a cookposition to control said elements to efiect a cooking operationincluding a bake operation and a broil operation and user settable in aclean position to control said elements to effect an accelerated thermalcleaning operation, said control means including a circuit connectingsaid bake and broil heating elements to a source of electrical power, anoven temperature thermostat connected in said circuit and presettablethroughout an oven temperature range in said cook position forcontrolling the energization of said bake and broil elements in acycling mode during said bake operation, and presettable in a fixedbroil setting in said cook" position for controlling the energization ofsaid broil element for normally continuous operation during said broiloperation but adapted to cycle said broil element at an oven temperaturein excess of substantially 600 F., said thermostat including a sensorsupported adjacent said top wall for sensing oven temperature thereat,said circuit includinga double pole-double throw transfer switchinterconnected in series electrical circuit between said thermostat andsaid elements for connecting said elements in said cook" position forsaid cooking operation, and said transfer switch operative forconnecting said elements in said clean position such that when saidthermostat is set in said broil" setting said circuit provides fullwattage to said bake element and no wattage to said broil elementwhereby said bottom wall is heated to an accelerated F., a bakingelement'supported adcleaning temperature by said bake element while saidthermostat functions to cycle said bake element to prevent the oventemperature at said sensor from exceeding substantially 600 F. duringthe accelerated thermal cleaning operation.

- .2. A continuously-cleaning oven as recited in claim 1 wherein thethermostat sensor is in the formof an hydraulic diaphragm bulb.

3. A continuously cleaning oven comprising an outer oven housingenclosing walls defining a bake and broil compartment, said compartmenthaving a bottom' wall, opposite side walls, a door for closingsaid'compartment, a rear wall and a top wall, a thermal cleaning coatinghaving the characteristic of oxidizing oven food soils thereon in theoven temperature range of between 400 and 600 F. on the exposed surfaceof at least said bottom wall, a baking element supported adjacent thebottom wall and a broiling element supported adjacent the top wall ofthe compartment, control means for said baking and broiling elementssettable in a cook position to control said elements to effect a cookingoperation including a bake operation and a broil operation and usersettable in a clean position to control said elements to effect anaccelerated thermal cleaning operation, said control means including acircuit connecting said bake and broil heating elements to a source ofelectrical power, an oven temperature thermostat having first and secondcycling contacts connected in said circuit and presettable throughout anoven temperature range in said cook" position for controlling theenergization of said bake and broil elements in a cycling mode duringsaid bake operation and presettable in a fixed broil setting in saidcook position for controlling the energization of said broil element fornormally continuous operation during said broil operation but adapted tocycle said broil element at an oven temperature in excess ofsubstantially 600 F., said thermostat including an hydraulic sensingbulb supported adjacent said top wall for sensing oven temperaturethereat, said control circuit including first and second line conductorsand a neutral conductor connected to said source of power; said oventemperature thermostat having first and second cycling switchescontrolled by said bulb and operative with said cycling contacts so asto be responsive to temperatures in said oven compartment; said controlmeans including a pair of interconnected transfer switches in the formof a double pole-double throw switch, first circuit means connectingsaid first line conductor and said first thermostat cycling contact to ajunction of said broil heating element and said bake heating element,said broil heating element having its other side connected to one switchof said pair of interconnected transfer switches, said bake heatingelement having its other side connected to the other switch of said pairof interconnected transfer switches, second circuit means connectingsaid second line conductor and said second thermostat cycling switch toa junction of a first fixed thermostat bake contact-and a fixed broilcontact, said first fixed bake contact connected via a first movablebake contact to one cook" contact of said transfer switch, said fixedbroil contact connected via a double throw movable contact to the othercook contact of said transfer switch, third circuit means connectingsaid neutral conductor to a second fixed bake contact; said second bakecontact connected via said double throw movable contact to said othercook contact of said transfer switch, said one cook" contactelectrically connected to an opposite clean contact of said transferswitch; said other cook contact electrically connected to an oppositeclean contact of said transfer switch thereby connecting said heatingelements in a cook" circuit to provide alternatively full cycling powerto said broil element or cycling power to said bake element and saidbroil element, said interconnected transfer switches operative forconnecting said elements in a clean circuit such that when saidthermostat is set in said broil setting said circuit provides fullwattage to said bake element and no wattage to said broil elementwhereby said oven bottom wall is heated to an accelerated cleaningtemperature while said thermostat functions to cycle said bake elementto prevent the oven temperature at said sensor from exceedingsubstantially 600 F. during the accelerated thermal cleaning operation.

1. A continuously cleaning oven comprising an outer oven housingenclosing walls defining a bake and broil compartment, said compartmenthaving a bottom wall, opposite side walls, a door for closing saidcompartment, a rear wall and a top wall, a thermal cleaning coating onthe exposed surface of at least said bottom wall, and having thecharacteristic of oxidizing oven food soils thereon in the oventemperature range of between 400* and 600* F., a baking elementsupported adjacent the bottom wall and a broiling element supportedadjacent the top wall of the compartment, control means for said bakeand broil elements settable in a ''''cook'''' position to control saidelements to effect a cooking operation including a bake operation and abroil operation and user settable in a ''''clean'''' position to controlsaid elements to effect an accelerated thermal cleaning operation, saidcontrol means including a circuit connecting said bake and broil heatingelements to a source of electrical power, an oven temperature thermostatconnected in said circuit and presettable throughout an oven temperaturerange in said ''''cook'''' position for controlling the energization ofsaid bake and broil elements in a cycling mode during said bakeoperation, and presettable in a fixed ''''broil'''' setting in said''''cook'''' position for controlling the energization of said broilelement for normally continuous operation during said broil operationbut adapted to cycle said broil element at an oven temperature in excessof substantially 600* F., said thermostat including a sensor supportedadjacent said top wall for sensing oven temperature thereat, saidcircuit including a double pole-double throw transfer switchinterconnected in series electrical circuit between said thermostat andsaid elements for connecting said elements in said ''''cook'''' positionfor said cooking operation, and said transfer switch operative forconnecting said elements in said ''''clean'''' position such that whensaid thermostat is set in said ''''broil'''' setting said circuitprovides full wattage to said bake element and no wattage to said broilelement whereby said bottom wall is heated to an accelerated cleaningtemperature by said bake element while said thermostat functions tocycle said bake element to prevent the oven temperature at said sensorfrom exceeding substantially 600* F. during the accelerated thermalcleaning operation.
 2. A continuously-cleaning oven as recited in claim1 wherein the thermostat sensor is in the form of an hydraulic diaphragmbulb.
 3. A continuously cleaning oven comprising an outer oven housingenclosing walls defining a bake and broil compartment, said compartmenthaving a bottom wall, opposite side walls, a door for closing saidcompartment, a rear wall and a top wall, a thermal cleaning coatinghaving the characteristic of oxidizing oven food soils thereon in theoven temperature range of between 400* and 600* F. on the exposedsurface of at least said bottom wall, a baking element supportedadjacent the bottom wall and a broiling element supported adjacent thetop wall of the compartment, control means for said baking and broilingelements settable in a ''''cook'''' position to control said elements toeffect a cooking operation including a bake operation and a broiloperation and user settable in a ''''clean'''' position to control saidelements to effect an accelerated thermal cleaning operation, saidcontrol means including a circuit connecting said bake and broil heatingelements to a source of electrical power, an oven temperature thermostathaving first and second cycling contacts connected in said circuit andpresettable throughout an oven temperature range in said ''''cook''''position for controlling the energization of said bake and broilelements in a cycling mode during said bake operation and presettable ina fixed ''''broil'''' setting in said ''''cook'''' position forcontrolling the energization of said broil element for normallycontinuous operation during said broil operation but adapted to cyclesaid broil element at an oven temperature in excess of substantially600* F., said thermostat including an hydraulic sensing bulb supportedadjacent said top wall for sensing oven temperature thereat, saidcontrol circuit including first and second line conductors and a neutralconductor connected to said source of power; said oven temperaturethermostat having first and second cycling switches controlled by saidbulb and operative with said cycling contacts so as to be responsive totemperatures in said oven compartment; said control means including apair of interconnected transfer switches in the form of a doublepole-double throw switch, first circuit means connecting said first lineconductor and said first thermostat cycling contact to a junction ofsaid broil heating element and said bake heating element, said broilheating element having its other side connected to one switch of saidpair of interconnected transfer switches, said bake heating elementhaving its other side connected to the other switch of said pair ofinterconnected transfer switches, second circuit means connecting saidsecond line conductor and said second thermostat cycling switch to ajunction of a first fixed thermostat bake contact and a fixed broilcontact, said first fixed bake contact connected via a first movablebake contact to one ''''cook'''' contact of said transfer switch, saidfixed broil contact connected via a double throw movable contact to theother ''''cook'''' contact of said transfer switch, third circuit meansconnecting said neutral conductor to a second fixed bake contact; saidsecond bake contact connected via said double throw movable contact tosaid other ''''cook'''' contact of said transfer switch, said one''''cook'''' contact electrically connected to an opposite ''''clean''''contact of said transfer switch; said other ''''cook'''' contactelectrically connected to an opposite ''''clean'''' contact of saidtransfer switch thereby connecting said heating elements in a''''cook'''' circuit to provide alternatively full cycling power to saidbroil element or cycling power to said bake element and said broilelement, said interconnected transfer switches operative for connectingsaid elements in a ''''clean'''' circuit such that when said thermostatis set in said ''''broil'''' setting said circuit provides full wattageto said bake element and no wattage to said broil element whereby saidoven bottom wall is heated to an accelerated cleaning temperature whilesaid thermostat functions to cycle said bake element to prevent the oventemperature at said sensor from exceeding substantially 600* F. duringthe accelerated thermal cleaning operation.